Device for phase-synchronization of several laser oscillators

ABSTRACT

A device for phase synchronization of several laser oscillators characterized by several partial laser oscillators, each of which has active material and a first reflecting mirror, being arranged with a common second reflecting mirror to complete the resonators of each partial oscillator, and an optical component which is disposed between the common second mirror and the active material of each partial oscillator for phase coherent superposing the partial waves from each partial oscillator to create a single summation wave which is phase synchronized and coherent. The optical component can be a grating or a hologram which is preferably a volume phase hologram. The device is particularly useful for providing a pumping device for a solid state laser which device uses semiconductor lasers.

United States Patent [191 Roess Oct. 2, 1973 [75] Inventor: DieterRoess, Planegg Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin& Munich, Germany [22] Filed: June 12, 1972 {21] Appl. No.: 261,941

[30] Foreign Application Priority Data June 29, l97l Germany P 2l 3228l.6

[52] U.S. Cl. 331/945 [51] Int. Cl. 1101s 3/08 [58] Field of Search33l/94.5

[56] References Cited UNITED STATES PATENTS 3,577,093 5/l97l Simpson331/945 3,435,371 3/1969 White 33l/94.5

Primary ExaminerWilliam L. Sikes Attorney-Benjamin H. Sherman et al.

57 ABSTRACT A device for phase synchronization of several laseroscillators characterized by several partial laser oscillators, each ofwhich has active material and a first reflecting mirror, being arrangedwith a common second reflecting mirror to complete the resonators ofeach partial oscillator, and an optical component which is disposedbetween the common second mirror and the active material of each partialoscillator for phase coherent superposing the partial waves from eachpartial oscillator to create a single summation wave which is phasesynchronized and coherent The optical component can be a grating or ahologram which is preferably a volume phase hologram. The device isparticularly useful for providing a pumping device for a solid statelaser which device uses semiconductor lasers.

8 Claims, 1 Drawing Figure DEVICE FOR PIIASE-SYNCHRONIZATION OF SEVERALLASER OSCILLATORS BACKGROUND OF THE INVENTION 1. Field of the InventionThe present invention is directed to a device for producing a phasesynchronized summation wave from the waves of several laser oscillators.

2. Prior Art In a laser, particularly a laser diode, theamplification ofthe electromagnetic performance is based on the utilization ofabsorption and emission procedure in the laser material. Since theinternal energy of material is only present in specific energy levelswhich levels are the energy levels assumed by particles such as atoms,molecules or electrons, the release or the acceptance of energy by thematerial generally takes place in discreet amounts of energy. Thesediscreet amounts of energy are determined by the energy distancesbetween respective energy levels which levels participate in the energyrelease or acceptance. The energy distance between two levels E,, and E,is given by the relationship: E E,,=hv, where h is Plancks constant andu is a frequency determined by the difference between the two energylevels. According to this relationship, if an energy of hu is absorbedby a particle in the energy level 1-3,, the particle will move to ahigher energy level E During release of energy, the particle which is inthe energy level E,, releases radiation energy hu as it moves or returnsto a lower energy level [3,.

If the phase and direction of the emitted radiation energy aredifferent, a so-called spontaneous emission occurs which is incoherentand not suitable for amplification. The spontaneous emission is thereason for noise.

The amplification mechanism is based on so-called induced emission whichis obtained by the following procedure. If a radiation quantum hvstrikes a stimulated particle in the energy level E,,,, the particle canpass into the lower energy level E,. by emitting a radiation quantum hv.However, in this case both energy quanta have the same phase anddirection unlike the case of spontaneous emission. The electromagneticradiation is coherent and reinforced because of the quantum doubling. i

In the optical area, simple energy sources, whose radiation have thesame frequency and the same phase, are not available with sufficientperforance. Therefore, the quantum transitions which are caused by thelight energy do not take place in the same phase. By utilizing amultitude of equal-phase pump-energy sources of the same frequency suchas a plurality of laser diodes, it is a possibility to increase the pumpperformance for a laser having an extended crystal laser material.However, the laser diodes must be synchronized in phase.

SUMMARY OF THE INVENTION The present invention is directed to a devicewhich makes a phase-like synchronization of several laser oscillatorspossible. This is accomplished with a device comprising several partiallaser oscillators with each oscillator having active material and afirst reflector which partial oscillators are arranged with a secondreflector to complete the resonator of each oscillator. To provide asingle summation wave, which is coherent and phase synchronized, meanssuch as a coherent optical component is arranged between the secondreflec- BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematicillustration of the device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The principles of the presentinvention are particularly useful in a device illustrated in the FIGUREwhich has a pair of partial laser oscillators 1 and 2, for examplesemiconductor lasers, which includes a laser-active material havingelectrodes for applying a pumping energy to the material in aconventional manner and a first reflector 3 and 4, respectively. Thedevice further includes means, such as a coherent optical component 5,for superposing the partial waves from the partial oscillators l and 2as a single summation wave, which is coherent and phase-synchronized,onto a second reflector 6. The second reflector 6, which may bepartially permeable to enable removal of the superimposed wave in aconventional manner, is a common reflector for the two partialoscillators l and 2 and completes the resonator structure for theseoxcillators.

The coherent optical component can be a grating which is preferablyprovided as a hologram. The hologram should be a volume phase hologrambecause of its high efficiency.

The principle of the invention is based on the recognition that byuniting the beams of different partial resonators by means of acomponent, which has the characteristic to create a phase-coherentsuperimposing of its partial waves as one single summation wave which issimply defined in amplitude and phase, all partial beams or waves haveto be coherent. In such a system each single oscillator has the lowestthreshold, and if it preoscillates with all other oscillators in aphasecoherent way, a coherent oscillation of all partial systems willnecessarily result from the noise.

Preferably the coherent optical component is a hologram which reveals aninterference structure or pattern. The hologram is created bysuperimposing a spherical wave with a series of spherical waves from thevarious single resonators of the partial oscillators and the hologram islocated at the beam waist of the superimposed spherical waves. Such ahologram reconstructs a plane wave by means of illumination with amultitude of identical coherent partial waves and the plane wave isreflected back by the common second reflector into the system. In thecase of an incoherent partial wave, a complicated spacial refractionpattern with timewise fluctuations is created and only a slight fractionof the refraction pattern is reflected back from the common reflector.

The coherent optical component 5 can be realized as a hologram for arandom number of partial laser oscillators. If a volume phase hologramis used as the coherent optical component 5, an efficiency of nearlypercent can be achieved and a large variety of types of laseroscillators can be phase synchronized.

The device of the invention is especially well suited for providing thepumping means in a laser having a solid state laser body disposed in aresonator. The laser body such as a crystal laser can be pumped axiallyby the device utilizing a large number of semiconductor lasers.

Although minor modifications might be suggested by those versed in theart, it should be understood that I wish to employ within the scope ofthe patent granted hereon, all such modifications that reasonably andproperly come within the scope of my contribution to the art.

1 claim:

1. A device for providing a single phase synchronized laser wave,comprising several partial laser oscillators with each oscillator havingactive material for producing a partial wave and a first reflector, asecond reflector arranged with the partial oscillators to provide acommon second reflector to complete the resonator and each oscillator,and means comprising a hologram disposed between a common reflector andthe active material of each partial oscillator for phase-coherentsuperposing the partial waves from each of the partial oscillators tocreate a single, phase-synchronized coherent summation wave.

2. A device according to claim 1, wherein the hologram is a grating.

3. A device according to claim 2, wherein the hologram is a volume phasehologram.

4. A device according to claim 2, wherein the hologram is aninterference structure which is created by superposing an approximatespherical wave with a series of spherical waves of the various partialresonators with the hologram located at the beam waist of the superposedwaves.

5. A device according to claim 1, wherein the hologram is aninterference structure which is created by superposing an approximatespherical wave with a series of spherical waves of the various partialresonators with the hologram located at the beam waist of the superposedwaves.

6. A device according to claim 1, wherein the hologram is a volume phasehologram.

7. A device according to claim 6, wherein the hologram is aninterfrerence structure which is created by superposing an approximatespherical wave with a series of spherical waves of the various partialresonators with the hologram located at the beam waist of the superposedwaves.

8. In a laser device having a solid state laser body disposed in aresonator and means for pumping the laser body the improvementcomprising the pumping means comprising several partial oscillators witheach oscillator having active material for producing a partial wave anda first reflector, a second reflector to complete the partial resonatorsand each of the oscillators, and means disposed between the commonsecond reflector and the active material of each partial oscillator forphase-coherent superposing the partial waves for each of the partialoscillators to create a single phase synchronized, coherent summationwave for axially pumping the solid state laser body.

1. A device for providing a single phase synchronized laser wave,comprising several partial laser oscillators with each oscillator havingactive material for producing a partial wave and a first reflector, asecond reflector arranged with the partial oscillators to provide acommon second reflector to complete the resonator and each oscillator,and means comprising a hologram disposed between a common reflector andthe active material of each partial oscillator for phase-coherentsuperposing the partial waves from each of the partial oscillators tocreate a single, phase-synchronized coherent summation wave.
 2. A deviceaccording to claim 1, wherein the hologram is a grating.
 3. A deviceaccording to claim 2, wherein the hologram is a volume phase hologram.4. A device according to claim 2, wherein the hologram is aninterference structure which is created by superposing an approximatespherical wave with a series of spherical waves of the various partialresonators with the hologram located at the beam waist of the superposedwaves.
 5. A device according to claim 1, wherein the hologram is aninterference structure which is created by superposing an approximatespherical wave with a series of spherical waves of the various partialresonators with the hologram located at the beam waist of the superposedwaves.
 6. A device according to claim 1, wherein the hologram is avolume phase hologram.
 7. A device according to claim 6, wherein thehologram is an interfrerence structure which is created by superposingan approximate spherical wave with a series of spherical waves of thevarious partial resonators with the hologram located at the beam waistof the superposed waves.
 8. In a laser device having a solid state laserbody disposed in a resonator and means for pumping the laser body theimprovement comprising the pumping means comprising several partialoscillators with each oscillator having active material for producing apartial wave and a first reflector, a second reflector to complete thepartial resonators and each of the oscillators, and means disposedbetween the common second reflector and the active material of eachpartial oscillator for phase-coherent superposing the partial waves foreach of the partial oscillators to create a single phase synchronized,coherent summation wave for axially pumping the solid state laser body.